Gas sensors are sensors that sense gas and can be classified into categories of: catalytic combustion sensors, controlled potential electrolysis sensors, hot wire semiconductor sensors, metal oxide semiconductor sensors, etc.
Catalytic combustion sensors have low detection sensitivity and long response time and can sense gases only in high temperature environments.
Controlled potential electrolysis sensors have short life spans compared to other types of sensors.
Hot wire semiconductor sensors are fabricated on a silicon substrate. No gas sensors formed on silicon substrates can be operated in a high temperature environment due to a comparably low energy gap of silicon.
Metal oxide semiconductor sensors can be operated in high temperature and corrosive environments, have comparably short response time and low fabrication cost and can be easily combined with digital circuits to form a gas sensor network. Metal oxide semiconductor sensors are the most needed gas sensors and are widely used in almost every environment from homes to factories for sensing toxic or explosive gases.
However, conventional metal oxide semiconductor sensors have poor gas selectivity, i.e. can only sense a single gas instead of multiple gases simultaneously. Thus improving metal oxide semiconductor sensors to sense multiple gases simultaneously and maintain a good sensitivity is a research objective for researchers.